express in simplest form?

Question

(x - y + 1)(x + y)

Answer 1

Multiply it out, mayhaps.

x^2 +x + y - y^2

Which is also
x(x + 1) + y(1-y)

Why does this question have four answers below, ALL OF WHICH STATE THE SAME THING?

Answer 2

(x - y + 1)(x + y)
= x(x + y) -y(x + y) + 1(x + y)
= x^2 + xy -xy -y^2 + x + y
= x^2 -y^2 + x + y

Answer 3

x^2-xy+x+xy-y^2+y
x^2-Y^2+x+y
(x-y+1)(x+y)
i think you have given the simplest.i got the same one

Answer 4

(x-y+1)(x+y)
x(x+y)-y(x+y)+1(y+x)
x^2+xy-xy+y^2+x+y
x^2+y^2+x+y